GOAL: To provide a much-needed simple, valid, and reliable measure of dynamic thumb forces that quantifies functional performance, impairment and recovery related to orthopedic and neurological diseases. The absence of an objective and sensitive outcome measure of dynamic thumb forces precludes informative clinical studies to optimize the choice, timing and options of treatment for each patient. APPROACH: We have designed a novel test to quantify the ability to produce dynamic thumb forces. The strength-dexterity (S-D) test is based on the principle of buckling of slender springs, and its current prototype consists of asking a person to attempt to compress each of 87 compression springs with different combinations of strength (stiffness) and dexterity (propensity to buckling) requirements. Our past clinical work has shown that the S-D Test is repeatable and is informative of the neuro-musculo-skeletal integrity of thumb with carpometacarpal osteoarthritis (CMC OA) better than measurements of pinch strength. We propose to refine the S-D Test into a clinically useful measure of dynamic thumb forces. AIM 1: Minimize burden to patient and clinician. We will shorten the S-D Test from 87 spring compressions to compressing at most 2 springs, 3 times each. Digital signal processing of fingertip kinematics and sensors embedded in this spring will fully characterize dynamic neuro-musculo-skeletal thumb function at each strength level via 3 continuous parameters. AIM 2: Validate the shortened S-D Test against established measures of hand function. We will deploy the S-D Test at the Hospital for Special Surgery to test the following hypotheses. PRIMARY HYPOTHESIS: The S-D Test correlates with available measures of hand function. SECONDARY HYPOTHESIS: The S-D Test correlates with patient satisfaction after treatment for CMC OA better than available measures of hand function. IMPACT: We seek to develop an assessment tool that is both simple and expeditious to administer, and can divulge a more comprehensive/reliable and quantifiable measure of this crucial thumb function. Developing the S-D Test into a quick, objective, and clinically valid measure of dynamic thumb forces will be instrumental to quantifying impairment and assessing effectiveness of treatments in today's clinical environment.